1) Field of the Invention
The present invention relates to a power supply apparatus, and particularly, relates to apparatuses where electrical power consumption can be greatly reduced. The power supply apparatus according to the invention can be suitably applied to any electrical appliance having a remote controlling system, such as television equipment, video equipment, audio equipment and air conditioning systems; or electrical appliances, which should keep them in their standby mode even when the main functions of the appliance are not being used, such as telephone equipment, facsimile equipment and personal computers.
2) Related Arts
A remote controlling system is used in many kinds of electrical appliances, due to its convenience. Recently, such appliances are so designed that a main switch for turning on or off the main unit of these appliances is omitted and thus the appliances always keep their standby mode for receiving an on/off signal from the remote controller during the period when the main unit is not being used. Further, in some of these appliances, the main switch is omitted but a small sub-switch is equipped to switch the function mode between a standby mode and a driving mode. Appliances having a remote controlling system are always in a standby mode in order to watch and wait for a remote control signal; and the appliances having a sub-switch are also always in a standby mode so that it makes it possible to put the appliance in a driving mode each time even if the main unit of the appliance is not working. Therefore, these appliances always consume some electrical power when waiting for a signal even when the main units of the appliances do not work.
Telecommunication appliances, such as telephone equipment and facsimile equipment, should always keep themselves in a standby condition for telecommunication signals. Therefore, in order to keep the standby function, a certain amount of electrical power is always being consumed in these appliances.
The following four electrically conductive conditions are evidenced in an electrical appliance having a remote controlling function or a signal standby function.
(1) Complete off condition, which means a plug for connecting the appliance to the commercial AC power source is pulled off: PA1 (2) The plug is still connected to the commercial AC power supply, i.e. inserted into the power socket, but the main switch of the appliance is switched off: PA1 (3) The appliance is in a standby condition for a remote control signal or a telecommunication signal: PA1 (4) The appliance is in a driving condition, which means the main unit is working.
Under the condition (1) and (2), there is no problem because almost no current goes through the appliance, but under the condition (3), the amount of current, which is consumed in the standby condition for the remote control signal or the telecommunication signal, is not as small as we would expect. Because, the power supply apparatuses for use in electrical appliances are generally constructed such that only the main circuits provided in the secondary side of the transformer are switched OFF while keeping the circuits in the primary side of the transformer ON during the standby condition, so that some electrical current is always consumed at the primary inductance of the transformer and then so-called copper loss, which is Joule heat of the coil, and so-called iron loss, which is generated by eddy current in the magnetic cores, are generated. In the case, particularly, that the power supply apparatus is arranged as a switching regulator, a switching loss caused by the operation of a switching element is generated in addition to the copper loss and the iron loss.
In the conventional power supply apparatus, it is not enough to pay efforts to reduce such an electrical power consumption when the appliance is in the standby condition, but more effort is being paid to decrease the manufacturing cost for the appliances by making the circuit construction simpler. However, nowadays, it should also be important to save energy from a point of view of the environment of our earth, thus it is becoming an important matter to save the consumption of the electrical power which is wasted when the appliances are in a standby condition.
An electrical power supply apparatus where the above problem is solved has been disclosed, for instance, in Japanese Preliminarily Patent Publication No. HEI 8-130871. The apparatus disclosed in this publication is designed; when the main unit of the appliance is in a standby mode, a switching element is controlled so as to be operated intermittently in accordance with a standby signal in order to decrease the electrical current consumption when the main unit is in a standby mode.
Particularly, in the AC-DC converter which uses a commercial AC supply, the input voltage is about 100V in Japan, and after rectifying the voltage becomes about 140V. In this case, since only a small amount of voltage of about 10V, which is used for driving the control circuit for controlling the switching element is taken from such a high input voltage, an initiating resister having a large initiating resistance required to initiate the control circuit. Therefore, in the AC-DC converter, a significant amount of power is consumed by the initiating resistance, so that a sufficient effect for decreasing the power consumption cannot be obtained only by making the operation of the switching element intermittent.
Second, in the apparatus disclosed in the above-mentioned publication, when the operation of the switching element is conducted intermittently, the switching frequency comes down to about several kHz so that a discordant sound is generated from the transformer. Therefore, such an apparatus would have a problem if it is applied to the appliances for private demands, such as television equipment, video equipment, etc. In addition, in this apparatus, the operation of the switching operation is changed into the intermittent mode in response to a stand-by signal sent from the main unit. That is to say, the change is not done automatically.
Apparent from the apparatus disclosed in the above-mentioned publication, there is a conventional switching regulator using an RCC (Ringing Choke Converter) or in a certain kind of DC-DC converter, where the switching operation of the switching element naturally becomes intermittently when the load thereof becomes extremely small, depending on the design or adjustment of the circuit. In such a converter, the switching frequency comes down to several kHz when the switching operation becomes intermittently, so that a discordant sound is also generated from the transformer. Further, there is another problem that the "ripple" becomes great when the switching frequency comes down. In order to avoid these problems, in the conventional switching regulator using an RCC, or the conventional DC-DC converter, a bleeder resistance is generally provided to prevent the operation of the switching element from becoming intermittent. Therefore, in such an apparatus, much more electrical current is consumed by the bleeder resistance in addition to the certain amount of the electrical power wasted when the main unit is in a standby condition.